Note 3 - Financial Instruments Measured at Fair Value - Short-term Investments by Security Type (Details) - USD ($) $ in Thousands		Jun. 30, 2018	Dec. 30, 2017
Amortized Cost		$ 23,875	$ 21,338
Gross Unrealized Gains		1	1
Gross Unrealized Losses	[1]	11	10
Short-term investments		23,865	21,329	[2]
Corporate Debt Securities [Member]
Amortized Cost	[3]	10,849	12,784
Gross Unrealized Gains	[3]	1	1
Gross Unrealized Losses	[1],[3]	5	6
Short-term investments	[3]	10,845	12,779
US Treasury Securities [Member]
Amortized Cost		7,726	7,935
Gross Unrealized Gains
Gross Unrealized Losses	[1]	5	4
Short-term investments		7,721	7,931
Certificates of Deposit [Member]
Amortized Cost		3,750
Gross Unrealized Gains
Gross Unrealized Losses	[1]
Short-term investments		3,750
Debt Security, Government, Non-US [Member]
Amortized Cost		556	619
Gross Unrealized Gains
Gross Unrealized Losses	[1]
Short-term investments		556	$ 619
US Government-sponsored Enterprises Debt Securities [Member]
Amortized Cost		994
Gross Unrealized Gains
Gross Unrealized Losses	[1]	1
Short-term investments		$ 993

[1] As of June 30, 2018, there were $14.7 million of investments in our portfolio in a loss position. As of December 30, 2017, the cost and fair value of investments with loss positions were approximately $13.2 million. We evaluated the nature of these investments, credit worthiness of the issuer and the duration of these impairments to determine if an other-than-temporary decline in fair value had occurred and concluded that these losses were temporary and we have the ability and intent to hold these investments to maturity.

[2] Derived from December 30, 2017 audited financial statements

[3] Corporate debt securities include investments in financial and other corporate institutions. No single issuer represents a significant portion of the total corporate debt securities portfolio.